See superheater for the device used in steam engines. See Superheating for the physics process A superheater is a device in a Steam engine that heats the steam generated by the A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid.

In physics, superheating (sometimes referred to as boiling retardation, or boiling delay) is the phenomenon in which a liquid is heated to a temperature higher than its standard boiling point, without actually boiling. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid This can be caused by rapidly heating a homogeneous substance while leaving it undisturbed (in order to avoid the introduction of bubbles at nucleation sites). Nucleation is the onset of a Phase transition in a small region Superheated liquids can be stable above their usual boiling point if the pressure is above atmospheric (see superheated water). Superheated water is liquid Water under Pressure at temperatures between the usual Boiling point (100°C and the Critical temperature (374°C This article refers only to liquids above their actual boiling point in a metastable state

Contents 1 Mechanics 2 Myth 3 Scope restriction 4 References 5 See also 6 External links

Mechanics

With the exception of superheated water below the Earth's crust, a superheated liquid is usually the result of artificial circumstances. Metastability is a general scientific concept which describes states of delicate equilibrium Superheated water is liquid Water under Pressure at temperatures between the usual Boiling point (100°C and the Critical temperature (374°C Being such, it is metastable, and is disrupted once the circumstances abate, leading to the liquid boiling very suddenly and violently (a steam explosion). In the Physical sciences a phase is a Set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties A steam Explosion (also called a Littoral explosion, or fuel-coolant interaction, FCI) is a violent Superheating is sometimes a concern with microwave ovens, some of which can quickly heat water without physical disturbance. A microwave oven, or a microwave, is a Kitchen appliance that cooks or heats Food by Dielectric heating. Water is a common Chemical substance that is essential for the survival of all known forms of Life. A person agitating a container full of superheated water by attempting to remove it from a microwave could easily be scalded.

Superheating is common when a person puts an undisturbed cup of water into the microwave and heats it. Once finished, the water appears to have not come to a boil. Once the water is disturbed, it violently comes to a boil. This can be simply from contact with the cup, or the addition of substances like instant coffee or sugar, which could result in hot scalding water shooting out. Instant coffee is a beverage derived from brewed Coffee beans Through various manufacturing processes the coffee is dehydrated into the form of powder or granules The chances of superheating are greater with smooth containers, like brand-new glassware that lacks any scratches (scratches can house small pockets of air, which can serve as a nucleation point). Nucleation is the onset of a Phase transition in a small region

Rotating dishes in modern microwave ovens can also provide enough perturbation to prevent superheating.

There have been some injuries by superheating water, like when a person makes instant coffee and adds the coffee to the superheated water^[1]. This sometimes results in an "explosion" of bubbles. There are some ways to prevent superheating in a microwave oven, like putting a popsicle stick in the glass, or having a scratched container to boil the water in. However this is very, very rare and can only happen under certain conditions. A foreign object added to the water prior to heating, whether it be a plastic spoon or a salt cube, greatly diminishes the chance of an explosion because it provides nucleation sites.

Superheating also occurs in nuclear reactors and other types of high-temperature steam generators used for producing electricity, and is guarded against when it leads to corrosion or embrittlement of metal pipes.

Magnetrons, such as those used in microwave ovens, can also superheat steam in steam-power or steam-heating circuits, exponentially increasing steam thermal capacity. Advanced theories include powering the magnetron superheating circuit from electricity generated by the waste heat from the main steam circuit, resulting in additional heating BTUs for buildings at zero additional fuel cost or additional fossil fuel pollution.

Myth

A commonly mistaken belief is that superheating can only occur in pure substances. This is untrue because nucleation points for boiling do not include solid nucleation centres, but rather, seed-bubbles that occur due to the presence of solid nucleation centres. In other words, if there are solid nucleation centres in a substance (e. g. impure water) but without seed-bubbles (e. g. leaving impure water to stand or boiling it once to rid the water of the bubbles), superheating can occur^[2][3]. It is interesting to note however, that nucleation points for freezing include solid nucleation centres. That is to say, an impure substance cannot undergo supercooling.

Scope restriction

Milk and water with starch content do not boil over because of superheating, but rather result in extreme foam buildup. The most general definition of foam is a substance that is formed by trapping many gas Bubbles in a Liquid or Solid. This foam is stabilized by special substances in the liquids and therefore does not burst.

References

See also

• Supercooling
• Supersaturation
• Critical point
• Microwave oven
• Autoclave
• Boiling point

External links

• Video of superheated water in a microwave explosively flash boiling, why it happens, and why it's dangerous.
• A series of superheated water with oil film experiments done in the microwave by Louis A. Bloomfield, physics professor at the University of Virginia. Experiment #13 proceeds with surprising violence.
• Video of superheated water in a pot.Nucleation

Purified water is water from any source that is physically processed to remove impurities ***************************************************************************************** * * The term supersaturation refers to a Solution that contains more of the dissolved material than could be dissolved by the Solvent under normal circumstances In Physical chemistry, Thermodynamics, Chemistry and Condensed matter physics, a critical point, also called a critical state A microwave oven, or a microwave, is a Kitchen appliance that cooks or heats Food by Dielectric heating. An autoclave is a pressurized device designed to heat aqueous solutions above their Boiling point at normal atmospheric pressure to achieve sterilization The boiling point of a liquid is the temperature at which the Vapor pressure of the liquid equals the environmental pressure surrounding the liquid Nucleation is the onset of a Phase transition in a small region

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